[stella] Supercharger coding

Writing that last message about the FFF8 and FFF9 address on the
Supercharger reminded me of something that I'm not sure has ever been
announced on this list.

Bob Colbert and I put together what we believe to be a pretty good
description of how the Supercharger bankswitching and extra RAM works from
a programmers standpoint, and included it in the Cuttle Cart manual. If
you're interested in such things the Cuttle Cart manual is available online
at Atariage.com.